Process control of high density solder bumps by electroplating technology

In this paper, we describe the process control of high-density solder bumps by electroplating with high uniformity and repeatability. The die size is 10/spl times/10 mm and it has 1,520 total I/Os. The electroplated bump is composed of eutectic Sn/Pb with a pitch of 250 /spl mu/m and height of 100 /spl mu/m. Ti/Cu is used as the UBM (under bump metallurgy) which is deposited by sole sputtering. The nonuniformity of the bump heights is found to be less than 5% in a 6" wafer. The PR (photoresist) opening is 101/spl plusmn/1 /spl mu/m within wafers and 101/spl plusmn/2 /spl mu/m wafer-to-wafer. The deviation of the PR thickness is within /spl plusmn/2 /spl mu/m for a typical thickness of 45. The alignment accuracy is better than 1.5 /spl mu/m. The shear force of the UBM as sputtered is comparable to that incorporated with electroplated Cu reported in the literature. The reliability is investigated for different Cu thicknesses. The reliability test of high temperature storage at 150/spl deg/C shows that shear force remains constant for more than 650 hours and drops to one half of the original value after 2,000 hours for a 4 /spl mu/m sputtering Cu UBM. It is also found that the shear force does not decay after ten reflow cycles.